Data centers have to deal with large amounts of data while ensuring reliability, and typically employ redundant arrays of inexpensive disks (RAID) technology using multiple hard disk drives (HDDs) as storage devices (RAID devices). Some storage devices use solid state drives (SSDs), which are faster than HDDs. In SSDs, storage elements deteriorate because of writing and erasing of data. From the viewpoint of ensuring reliability, lifetime management such as load leveling is employed.
Examples of the related art are disclosed in Japanese Laid-open Patent Publication No. 2007-265265 and Japanese Laid-open Patent Publication No. 2011-150590.
However, RAID (a solid state drive group) including two or more SSDs has a possibility that multiple dead will occur. The multiple dead represents a state in which a plurality of SSDs reach their end of life at that same time. In particular, when leveling of the load on SSDs is performed, the risk of multiple dead occurring is higher in the solid state drive group.